This invention relates to the assignment of functions to assignable-function keys on a key telephone.
A typical key telephone system comprises a main unit, which performs certain control functions such as telephone call routing, and a plurality of key telephone sets connected to the main unit. Typically, the functions performed by corresponding keys on the various key telephone sets are identical, and all function keys are assigned a function. This arrangement simplifies the operation of the key telphone system but suffers the disadvantage that, when a new function is to be added, a new function key must be added to each key telephone set. Providing additional keys is extremely inconvenient, at best.
One way to overcome this problem would be uniformly to assign functions in advance to most, but not all, of the assignable-function keys on each set in the system, leaving the remainder of such keys to be assigned later in accordance with the individual user's special requirements. Pre-assigned keys might be, for example, the office line keys (those which connect the telephone set to the various outside lines) and the extension line keys (those which connect the telephone set to various intra-office extension lines). This arrangement would satisfy at least the minimum initial requirements for operation of the system and allow the flexibility to add special functions as necessary for individual sets, for example abbreviated dialing or hands-free operation. The disadvantage of this arrangement is that the programming of assignable-function keys which have not been assigned in advance must be done individually for each unassigned key on a telephone set. The assignment operation therefore takes a great deal of time, especially if the number of keys on each set which are not pre-assigned is large.
A similar difficulty arises in key telephone systems in which all telephones are not identical, i.e., the different sets have different numbers of assignable-function keys. In such a system, normally phones which are used more frequently will have more function keys and be assigned more office lines or special functions than other key telephone sets. The less frequently used telephone sets, having fewer function keys, are less expensive. As can be expected, however, much time is spent in assigning the various function keys in such a system, since the number of pre-assigned functions is necessarily limited to the smallest number of keys on any single keys telephone set. (Obviously, if even fewer keys are to be pre-assigned, much more work must be done to program the assignable-function keys.)
An additional difficulty in a key telephone system in which the telephone sets have varying numbers of assignable-function keys occurs when certain office lines are assigned to certain keys. Those office lines which are pre-assigned may be connected to all key telephone sets and are therefore much more heavily used than office lines which are individually assigned and may therefore be limited to only a few key telephone sets. The overall efficiency of office line use is therefore reduced.
In summary, the two principal difficulties with a key telephone system which uses telephones having varying numbers of assignable-function keys are that the operation of assigning the functions to the keys is very time-consuming and that the efficiency of using office lines is reduced.